This invention relates to a linear electro-mechanical actuator preferably for water cutting, which makes it possible to significantly improve the working conditions of the actuator, so as to optimise its load capacity and increase the working life of the of the actuator, and which makes it possible to reduce the risk of breakage or damage of the actuator following loss of control of the movement aimed at producing the force applied by the actuator.
Currently, the linear actuators for water cutting, or water jet, such as, for example, the one described in U.S. Pat. No. 9,212,657, have a motor, which may be, for example, electric, a shaft which acts as the rotor of the motor, a lead nut coupled to the rotor, and a translation unit, supported by a supporting structure, which may act as a casing for the actuator.
The motor may have permanent magnets, in which case the magnets are preferably mounted on the rotor shaft of the motor. The motor usually comprises a stator in which is situated the rotor shaft, preferably coaxially.
The translation unit comprises a screw, for example a recirculating ball screw, and at least a rod integral with the screw. The rod may have the purpose of pusher for generating at least a force in turn designed for generating the compression of at least one fluid.
The lead nut is coupled to the rotor shaft and is situated in the same rotor shaft coaxially with the same shaft. The screw is meshed with the lead nut, in the sense that it is coupled to the lead nut and situated in the lead nut coaxially with it, in such a way as to be also subjected, by the interposition of the lead nut and the rotor shaft, to the drive torque exerted by the motor.
The supporting structure comprises a main portion for housing the motor, the lead nut and the screw.
The actuator commonly also comprises an anti-rotation system or mechanism, which is such that the rotation of the lead nut, caused by the motor, generates the translation of the screw and the translation of the rod along a direction of translation. Under ideal conditions, the direction of translation is aligned with an axis of extension of the rod, which at least at one end is constrained to the screw.
This rotation the lead nut and the translation of the translation unit are preferably an alternating rotation and, respectively, an alternating translation.
Moreover, the actuator may be a single acting or a double-acting actuator. In the latter case, the translation unit usually comprises at least one further rod situated, along the axis of translation, on the opposite side of the screw relative to the rod described above.
Hereafter, for convenience, only a single rod connected to the screw is considered, even though all the following technical concepts can be applied to an actuator with more rods, and, as regards the features which relate to the rod, to each of them.
The alternating translation of the rod is such a way that the head portion of the rod, which comprises the end of the rod opposite the one at which the rod is constrained to the screw, generates the compression of the fluid located in a compression chamber. The compression chamber is advantageously defined at least partly by an interface portion of the supporting structure. The interface portion is adjacent to the main portion of the supporting structure, along the axis of translation of the rod, and is fixed to the main portion. The main portion and the interface portion are currently integrated in a single part.
The anti-rotation system may comprise, for example, a linear recirculating ball screw bearing.
The anti-rotation system is designed to exert an anti-rotation torque on the translation unit in such a way that the alternating rotation of the lead nut causes an alternating translation of the translation unit along the longitudinal axis of extension of the rod.
The anti-rotation system may comprise locking means designed to exert at least a part of the pair of anti-rotation torque on the translation unit. The locking means can also be designed to guide the translation of the translation unit along the direction of translation.
The anti-rotation system may comprise at least one linear bearing, for example a recirculating ball screw bearing, designed to guide the translation of the translation unit along the direction of translation.
The linear bearing may also be designed to exert at least a part of the anti-rotation torque on the translation unit.
The anti-rotation system therefore contributes, at least in part, to defining the direction of translation.
Under ideal conditions, which practically never occur, the axis of extension of the rod is aligned with the direction of translation.
The actuators currently known suffer from some problems regarding the possible misalignment which can easily occur between the axis of extension of the rod, which coincides with or in any case is at least parallel to that of the screw to which the rod is fixed, and the direction of translation defined by the anti-rotation system.
This misalignment is the cause of radial or lateral loads which act on the screw and in particular on the balls of a recirculating system of the screw, and which can also act on the anti-rotation system, and therefore on the balls of the anti-rotation system if it comprises a linear recirculating ball screw bearing.
These loads can cause an increase in the deterioration of the performance of the actuator, lowering the reliability of the actuator; as well as premature failures.